A161141 - OEIS

%I #11 Dec 05 2024 18:06:13

%S 1,3,9,27,33,81,99,243,297,333,729,891,999,1089,2187,2673,2997,3267,

%T 3333,6561,8019,8991,9801,9999,10989,19683,24057,26973,29403,29997,

%U 32967,33333,35937,59049,72171,80919,88209,89991,98901,99999,107811

%N Numbers which can be expressed as the product of numbers made of only threes.

%H Robert Israel, <a href="/A161141/b161141.txt">Table of n, a(n) for n = 1..10000</a>

%e 1 = empty product; 99 = 3 * 33; 1089 = 33 * 33; 999 = 3 * 333.

%p M:= 10^8: # for terms <= M

%p S:= {1}:

%p for d from 1 to ilog10(M) do

%p   x:= 3/9*(10^d-1); T:= {}:

%p   for s in S do

%p     T:= T union {seq(s*x^i,i=1..floor(log[x](M/s)))};

%p   od;

%p   S:= S union T;

%p od:

%p sort(convert(S,list)); # _Robert Israel_, Dec 05 2024

%Y Cf. A084034, A161140, A161142, A161143, A161144, A161145, A161146, A161147.

%K nonn,base

%O 1,2

%A _Claudio Meller_, Jun 03 2009

%E Corrected and extended by _Claudio Meller_, Jun 06 2009

%E 1 added by _N. J. A. Sloane_, Dec 04 2017